Polyphenylene sulfide films are conventionally used as F-class insulation thin material in variety of electric equipments and electric parts. Fine particles are often incorporated in the polyphenylene sulfide films in order to improve the slipping property of the film. Such a polyphenylene sulfide film containing the fine particles is manufactured by, as described in Japanese Patent Disclosure (Kokai) No. 34968/80, admixing the solid fine particles with the polypheneylene sulfide powder with a Henschel mixer or the like, stirring the resultant mix under fused condition to disperse the fine particles, and biaxially stretching the resulting polyphenylene sulfide resin composition under specific conditions. However, in the polyphenylene sulfide films prepared by this process, the dispersion of the fine particles is not uniform. As a result, not only is the slipping property of the film poor because of the large aggregations of the microparticles, but also insulation defects are likely to be formed especially in the case where the thickness of the film is not more than 10 .mu.m, so that the films have poor characteristics as dielectric films of capacitors. Further, when such a polyphenylene sulfide film is used as a base film of magnetic recording media such as floppy disks, drop out is likely to occur due to the large protrusion of the surface of the film. A polyphenylene sulfide film which has a good slipping property and high surface smoothness, and which has a reduced number of insulation defects, has not yet been obtained. DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to provide a polyphenylene sulfide film (hereinafter also referred to as "PPS film") which has excellent surface smoothness and slipping property, and which has a reduced number of insulation defects.
Another object of the present invention is to provide a capacitor which has excellent solder resistance, frequency characteristics and excellent thermal characteristics, and in which the distribution of the capacity and of the-withstand voltage is small.
Still another object of the present invention is to provide a magnetic recording media with which drop out rarely occurs and which has excellent dimensional stability and heat resistance.
Still another object of the present invention is to provide a process of producing a polyphenylene sulfide film which has excellent surface smoothness and slipping property, and which has a reduced number of insulation defects.
The present inventors intensively studied to find that a polyphenylene sulfide film containing fine particles with specific average particle size, which has a single particle index in a specific range, has excellent surface smoothness and slipping property, and have established a process of manufacturing this polyphenylene sulfide film to complete the present invention.
That is, the present invention provides a polyphenylene sulfide film which consists essentially of a resin composition containing polyphenylene sulfide as a major constituent, in which fine particles with an average particle size of 0.05-3 .mu.m are dispersed, the fine particles having a single particle index of not less than 0.5.
The present invention further provides a capacitor comprising e biaxially oriented polyphenylene sulfide film which consists essentially of a resin composition containing polyphenylene sulfide as a major constituent, in which fine particles with an average particle size of 0.05-3 .mu.m are dispersed, which fine particles have a single particle index of not less than 0.5, as a major dielectric material and an inner electrode made of a metal foil or a metal thin layer.
The present invention further provides a magnetic recording media comprising a biaxially oriented polyphenylene sulfide film which consists essentially of a resin composition containing polyphenylene sulfide as a major constituent, in which fine particles with an average particle size of 0.05-3 .mu.m are dispersed, which fine particles have a single particle index of not less than 0.5, and a magnetic layer formed on at least one surface of the polyphenylene sulfide film.
The present invention still further provides a process of producing polyphenylene sulfide film comprising the steps of mixing a slurry of fine particles containing the fine particles dispersed in a liquid medium with a boiling point of 180.degree.-290.degree. C. with polyphenylene sulfide powder such that the average particle size of the fine particles is not larger than 3 .mu.m, the amount of the fine particles being 1% by weight to 100% by weight with respect to the polyphenylene sulfide; supplying the resulting mixture to an extruder having at least one level of vent to fuse the polymer; eliminating the liquid medium of the slurry from the vent; and extruding the resulting polyphenylene sulfide in which the fine particles are dispersed to obtain a film in which the fine particles are dispersed.
The present invention still further provides a process of producing a polyphenylene sulfide film comprising the step& of supplying polyphenylene sulfide in a cylinder of an extruder having at least one level of vent; compulsively injecting into the cylinder of the extruder a slurry of fine particles containing fine particles dispersed in a liquid medium with a boiling point of 180.degree.-290.degree. C., which fine particles are dispersed in the liquid medium such that the average particle size thereof is not larger than 3 .mu.m, in the amount of 1% by weight to 100% by weight in terms of the fine particles with respect to the polyphenylene sulfide polymer before and/or after the polymer is fused; eliminating the liquid medium alone from the vent; and extruding the mixture of the polymer and the microparticles to produce a film in which the fine particles are dispersed.
The polyphenylene sulfide film of the present invention is excellent in slipping property and surface smoothness, and the number of the insulation defects in the film is reduced. The polyphenylene sulfide film has excellent heat resistance, dimensional stability and excellent electric characteristics, which are inherent to polyphenylene sulfide film. Thus, if the polyphenylene sulfide film of the present invention is used as dielectrics of a capacitor, a capacitor which has excellent solder resistance, frequency characteristics and excellent thermal characteristics, in which the distribution of the capacity and the withstand voltage are small, may be obtained. Further, if the polyphenylene sulfide film of the present invention is used as a base film of a magnetic recording medium, a magnetic recording medium with which the drop out rarely occurs may be obtained.